1. Field of the Invention
The present invention relates to a hydraulic braking system for use in an automotive vehicle, and more particularly to a hydraulic braking system having a recirculation type anti-skid apparatus.
2. Description of the Prior Art
As one of the hydraulic braking systems for automotive vehicles, Japanese Patent Laid-open Publication No. 61-282158, for example, discloses a system in which a recirculation type anti-skid apparatus including a fluid pump is disposed in a hydraulic circuit connecting a hydraulic pressure chamber of a master cylinder to a wheel brake cylinder.
In the above-described conventional system, a discharge passage of the fluid pump is connected to the hydraulic circuit between the hydraulic pressure chamber of the master cylinder and the wheel brake cylinder, and a brake fluid discharged from the fluid pump is recirculated to the hydraulic circuit. Therefore, in the anti-skid operation, a so-called kick-back phenomenon occurs and causes uncomfortable vibrations to a brake pedal with a discharge pulsation of the fluid pump transmitted to the master cylinder through the hydraulic circuit, and then to the brake pedal. Also, the vibrations or the like due to the discharge pulsation of the fluid pump cause a noise in a vehicle compartment.
The above problems may be dissolved by smoothening the discharge pulsation through an orifice which is disposed in the discharge passage of the fluid pump connected to the hydraulic circuit. For this purpose, the orifice must have a desired small-diameter. With such desired small-diameter orifice, however, a pressure load to the fluid pump is increased under a low temperature condition where the viscosity of brake fluid is high, so that durabilities of the fluid pump and a driving device for driving the fluid pump such as an electric motor are deteriorated. Further, the orifice is highly liable to be choked with a foreign matter. Therefore, if the orifice is choked with the foreign matter, the pressure load to the fluid pump is increased, so that the durability of the fluid pump or the like might be deteriorated.